Button with primary icon displays incorrectly

Description

When copying the jqueryui button demo (with icons) source code, the button containing only a primary icon displays incorrectly. The icon displays on one line, and then the button text displays on the next line.

The buttons look fine on the jqueryui site, but I cannot figure out why they do not work properly on my own site when using the demo code.

This is using a default jqueryui 1.8.4 download (overcast theme) and jquery 1.4.2